The Auto-Sentry is a small sentry gun that can be deployed by the player. It can be destroyed or will destroy itself after a short period of time. While deployed, it will shoot at any enemy target that comes in range.
It isn't a common sight in multiplayer games but it can be quite useful when used properly. It isn't as tough as a player and has no mobility so it can be an easy target. However, it can also be quite surprising. If you set up the sentry just out of sight, you can flank your enemy and push them into it. This frequently leaves them wondering where they were killed from.
Similarly, you can start a fire fight and then retreat, leaving the sentry to protect your back while you change positions to resume the fight.
